1-Worm/Yaha.K Virus

My Computer is infected with 1-Worm/Yaha.K virus. It happened after I tried to install Windows XP and had to visit Microsoft Compatibility Website. My AVG Antivirus software has been put out of Action by this virus. I cant run many programs incl. MS Word. I tried to download a free utility from www3.ca.com but it was not downloaded properly. onlinepcfix.com also offers a solution but at a cost of $16.
CAN ANYBODY HELP?